Query to get the min of the total

Hi All,

I am trying to do something but cannot find the way.
Hopefully you have some suggestions :)

I have two tables, as follows:

pets: with these columns: petcode, petname, petprice, petfamily
sales: with these columns: salescode, petcode, quantity

The pets table contains all the pets in my pet shop, with the code of the
pet, its name, its price and the family it belongs to.

So for example:

petcode | petname | petprice | petfamily
------------------------------------------------------------
1 | canary | 5.00 | birds
2 | retriever | 12.00 | dogs
3 | siamese | 28.00 | cats
4 | sparrow | 7.00 | birds
5 | poodle | 16.00 | dogs

The sales table tracks all the sales in the shop, with the code of the
sale, the code of the pet that was bought, and the quantity of this pet
bought.

For example:

salescode | petcode | quantity
----------------------------------------------
1 | 1 | 2
2 | 4 | 5
3 | 5 | 1
4 | 2 | 3
5 | 5 | 8
6 | 1 | 4

Now, I need to build a query that returns the least sold pet, in quantity.
It will include the pet name and the quantity sold.

So in the example above it will be:

petname | quantity
retriever | 3

Now, the problem I have is that I can´t work with nested aggregations.
First I need to get the total quantity by petcode (which will be the sum of
quantity). And then get the MIN of the SUM of quantity, which I don´t know
how to do.

This is the query so far:

SELECT
pets.petname,
sum(sales.quantity)

FROM sales INNER JOIN pets ON sales.petcode= pets.petcode

GROUP BY
pets.petname

HAVING SUM(sales.quantity)=(SELECT MIN(quantity) FROM sales)

ORDER BY pets.petname;

But it does not return any result. How can I do it?

Thanks very much